This application is based on Japanese Patent Application Nos. 2000-133616, 2000-332716 and 2001-93174 filed on May 2, 2000, Oct. 31, 2000 and Mar. 28, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The invention relates to a temperature control apparatus that adjusts the temperature of a heating medium supplied to a load or the temperature of the load itself.
2. Description of the Related Art
For processes of manufacturing liquid crystal panels or semiconductors, it is an essential requirement to be able to control temperatures, so that various temperature control devices are used. Some of those temperature control devices use brine supply devices. This kind of brine supply devices supply a temperature controlled heating medium, i.e., brine, to a load circuit, where the works, such as LCD panels, are disposed as a load, in order to maintain the temperature of the works constant.
For example, the Publication of Unexamined Japanese Patent Application No. JP-A-11-183005 disclosed a brine supply device consisting of a primary circuit that adjusts the brine temperature to a specified temperature, a secondary circuit that adjusts the brine temperature supplied to the works to a target temperature, and a valve that adjusts the flow rate of the brine that flows in from the primary circuit to be mixed with the flow of the secondary circuit. In this device, the valve opens when the work temperature rises above the preset temperature and causes the cooler brine from the prime circuit to be mixed at a predetermined flow rate with the secondary circuit brine. This lowers the temperature of the brine being supplied to the works to the preset temperature.
The PID control and the cascade control that combines two PID controls are the two most widely used control methods for controlling the above-mentioned valve in order to achieve the temperature control. In order to achieve a good control result by the PID control, it is necessary to tune P (proportional band), I (integral time), and D (differential time) constants to their optimum values. The PID constants are determined by means of a trial-and-error method while making a trial run of the device.
In the control of the valve operation, the variation xcex94MV of the manipulated variable MV obtained by PID calculations and the variation xcex94PV of the temperature are not proportional to each other. Therefore, a good control result is not obtainable by applying only one set of the PID constants within the temperature range to be controlled. Therefore, the temperature range to be controlled is divided into multiple segments and PID constants are determined for each temperature range segment. The problem here is that the tuning process becomes more complex and requires a longer time to complete as multiple sets of PID constants have to be determined.
In a process such as the one found in a semiconductor manufacturing system, a large heat load can be supplied to the work within a short time interval from an external heat source provided on said process side, or abruptly taken away. It is a system""s requirement to maintain the work temperature at the predetermined temperature at all times despite these heat load variations from the external heat source.
In case of feedback control systems such as the PID control system, the work temperature change according to the heat quantity variation is small if the change of heat load applied to the work is small, so that the work temperature can be maintained at the predetermined temperature with a sufficient accuracy.
However, in a feedback control system it is impossible to make the brine supply temperature change quick enough to follow the work temperature change if a large heat load change is made within a short period of time, which causes a hunting and instability of the control system in adjusting the work temperature to the predetermined temperature.
The present invention was made under the circumstances described above and its objective is to provide a temperature control device that can accurately control temperatures using only one set of PID constants.
The other objective is to offer a work temperature control device with an improved stability in adjusting the load to a predetermined temperature minimizing the probability of causing load temperature hunting phenomena.
The abovementioned object of this invention can be achieved with the following means.
The present invention is a temperature control device characterized by comprising:
a primary circuit for adjusting the temperature of a first heating medium to a predetermined temperature;
a secondary circuit for adjusting the temperature of a second heating medium, which is to be supplied to a load, to a target temperature (SV(S));
a valve for adjusting the flow rate of the first heating medium, which is to be mixed with the second heating medium or conducts a heat exchange with the second heating medium;
a supply temperature detection unit for detecting the current supply temperature (Pt1) of the second heating medium;
a PID arithmetic unit for calculating the manipulated variable (MV) of said valve based on the target temperature (SV(S)) of the second heating medium, the current supply temperature (Pt1) of the second heating medium, and a predetermined set of PID constants;
a compensating arithmetic unit for calculating a compensated manipulated variable (MVxe2x80x2) by compensating the manipulated variable (MV) calculated by said PID arithmetic unit; and
a control unit for controlling the operation of said valve based on the compensated manipulated variable (MVxe2x80x2); wherein
the variation (xcex94MV) of the manipulated variable (MV) is made proportional to the variation (xcex94PV) of the current supply temperature (Pt1) of the second heating medium by means of controlling the operation of said valve based on the compensated manipulated variable (MVxe2x80x2).
The compensating factor k (0xe2x89xa6kxe2x89xa61), by which the manipulated variable (MV) is multiplied at the compensation arithmetic unit, is defined as follows:
k=1xe2x88x92(Pt1xe2x88x92PV1)(1xe2x88x92n)/(PV2xe2x88x92PV1)
where,
PV1: lower limit of the operating temperature of the second heating medium;
PV2: upper limit of the operating temperature of the second heating medium;
Pt1: current supply temperature of the second heating medium; and
n: a constant for limiting the manipulated variable when the second heating medium supply temperature is equal to the upper limit PV2.
According to the temperature control unit described above, the supply temperature of the second heating medium can be adjusted to a desired temperature by means of only one set of PID constants for a wide temperature range from the lower limit to the upper limit of the operating temperature of the second heating medium. Consequently, it becomes possible to adjust the load to a predetermined temperature by means of only one set of PID constants. Since it is required to determine only one set of PID constants, the determination process can be easily performed and the user can easily change the setup temperature of the load.
The present invention is a temperature control device that maintains the temperature of the load to a setup temperature (SV(R)), while the heat load added thereto by an external heat source is changed, comprising:
a supply temperature detection unit for detecting the current supply temperature (Pt1) of a heating medium supplied to the load;
a load temperature detection unit for detecting the current temperature (Pt2) of the load;
an adjusting unit for adjusting the supply temperature (Pt1) of the heating medium;
an acquiring unit for acquiring in advance a first temperature change curve (L1) of the load when said heat load is changed while maintaining the supply temperature (Pt1) of the heating medium constant;
a first calculating unit for calculating an imaginary second temperature change curve (L2) of a load (W), which is in axial symmetry with said first temperature change curve (L1), based on the setup temperature (SV(R)) of the load;
a second calculating unit for calculating a target temperature change curve (L3) of the heating medium for realizing said second temperature change curve (L2); and
a control unit for controlling said adjusting unit so that the supply temperature (Pt1) of the heating medium changes according to said target temperature change curve (L3) when the heat load applied to the load by said external heat source is changed.
According to the temperature control unit described above, since the supply temperature of the heating medium is adjusted predictively before a temperature change occurs in the load due to the heat load change, the difference between the load temperature and the setup temperature does not grow as large as in feedback controls such as the PID control. Consequently, the load temperature can be maintained constant with a smaller hunting compared to the feedback control even when a large heat load change occurs in a short period of time, thus making it possible to achieve a higher control stability in adjusting the load to a setup temperature.